Unless otherwise indicated herein, approaches described in this section are not prior art to the claims listed below and are not admitted to be prior art by inclusion in this section.
An antenna is an electrical device which converts electric power into radio waves, and vice versa. Antennas are essential components of equipment and apparatuses that use radio or otherwise configured for wireless communication. Typically, an antenna includes an arrangement of metallic elements electrically connected to a transmitter and/or a receiver. During a transmission operation, an oscillating current of electrons forced through the antenna by a transmitter creates an oscillating electromagnetic (EM) field around the antenna elements. For a slot antenna such as those used in handheld applications, the maximum EM field is usually observed on an open end of the slot antenna, as shown in scenario 700A of FIG. 7. During a receiving operation, oscillating EM fields of an incoming radio wave exert force on electrons in the antenna elements to cause the electrons to move back and forth, thereby creating oscillating currents in the antenna. However, often times in handheld applications (e.g., mobile phones such as smartphones) the outgoing and incoming radio signals may be blocked by the hand and/or head of the user of the mobile phone, and this tends to significantly degrade the efficiency of the slot antenna. For example, in scenario 700B shown in FIG. 7, radio signals may be blocked by the hand of a user and thus the efficiency of slot antenna may be significantly degraded.
Further example scenarios of negative impact on antenna efficiency by hand and/or head of a user are illustrated in FIG. 8. For illustrative purpose, each scenario shown in FIG. 8 involves a handheld apparatus, e.g., a smartphone, with a top slot antenna and a bottom slot antenna. In scenario 800A, the handheld apparatus is held by a left hand of the user, resulting in good radio signals for the top slot antenna and poor radio signals for the bottom slot antenna. In scenario 800B, the handheld apparatus is held by a right hand of the user, resulting in good radio signals for both the top slot antenna and the bottom slot antenna. In scenario 800C, the handheld apparatus is held by the left hand of the user and is next to the head of the user, resulting in worse radio signals for the top slot antenna and poor radio signals for the bottom slot antenna. In scenario 800D, the handheld apparatus is held by the right hand of the user and is next to the head of the user, resulting in worse radio signals for the top slot antenna and good radio signals for the bottom slot antenna. In the example scenarios illustrated in FIG. 8, the terms “good”, “worse” and “poor” define the quality of radio signals from high to low in order. In other words, the quality of “good” radio signals is better than the quality of “worse” radio signals, which is better than the quality of “poor” radio signals.
An existing approach to address this issue is illustrated in FIG. 9. This approach utilizes an antenna swapping scheme. In a pass-through mode under the antenna swapping scheme as shown in part (A) of FIG. 9, a bottom slot antenna (antenna 0) at or near a bottom distal end of a handheld apparatus 900, e.g., smartphone, is used for wireless transmission and receiving until efficiency of the bottom slot antenna is degraded due to blockage by the hand and/or head of the user, at which time the wireless transmission and receiving may be switched to a swapping mode, shown in part (B) of FIG. 9, to be performed through a top slot antenna (antenna 1) at or near a top distal end of the handheld apparatus 900 opposite the bottom distal end. Nevertheless, as shown in FIG. 9 that the open end of each of bottom and top slot antennas is on the same side of the handheld apparatus 900 (i.e., the right side as shown in FIG. 9), performance of the antennas may be even worse when the handheld apparatus 900 is held by the left hand and close to the head of the user. Moreover, there is the issue of specific absorption rate (SAR) while in the swapping mode. Besides, trace loss of the top slot antenna is rather high.